Metal soaps are normally produced by directly reacting metal oxides or metal hydroxides with the corresponding organic carboxylic acids or by double decomposition where metal soaps are precipitated from hot aqueous or aqueous/alcoholic soap solution by addition of salt solutions of the particular metals (see, for example, Ullmann""s Encyklopxc3xa4die der Technischen Chemie, 4th Edition, Vol. 21, page 224).
EP-B-0 234 149 describes a process for the production of superbasic calcium soaps in which an oxide and/or a hydroxide of calcium is/are reacted with carbon dioxide, which is injected into the reaction medium, and at least one organic carboxylic acid in the presence of at least one promoter and at least one catalyst and the water formed is removed, the reaction being carried out in an least one organic solvent at temperatures of 80 to 120xc2x0 C., the organic carboxylic acid containing 7 to 13 carbon atoms and having a linear acid content of 40% by weight or less, a content of acids branched at C-2 of 20% by weight or less and a content of acids branched at C-3 and/or C-n of 40% by weight or more and the organic solvent being replaced by an oil or a mixture of oils at the end of the reaction. The promoter is intended to bind the carbon dioxide.
WO 95/34524 describes a process for the production of superbasic zinc soaps in which a zinc oxide and/or hydroxide is reacted while stirring with gaseous carbon dioxide and at least one organic carboxylic acid. The reaction takes place in the presence of at least one promoter which is intended make carbon dioxide easier to bind. In addition, the water formed during the reaction is said to be continuously removed. The reaction is preferably carried out at temperatures of 80 to 120xc2x0 C. and in the presence of at least one organic solvent.
The present invention relates, in general, to processes for the production of superbasic zinc soaps in which basic zinc carbonate and an organic carboxylic acid are directly reacted with one another. The processes may be conducted in the absence of organic solvents. The superbasic zinc soaps produced in accordance with the process of the present invention are useful as additives in plastics processing.
It has now been found that superbasic zinc soaps can readily be obtained by directly reacting zinc hydroxycarbonate (basic zinc carbonate) with organic carboxylic acids. The reaction is carried out at temperatures in the range from 100 to 200xc2x0 C.
The present invention relates to a process for the production of superbasic zinc soaps, characterized in that zinc hydroxycarbonate is reacted with organic carboxylic acids containing 6 to 22 carbon atoms at temperatures of 100 to 200xc2x0 C. in the absence of organic solvents and the water of reaction formed is continuously distilled off.
The process according to the invention can be carried out much more easily than the processes known from the prior art. In particular, there is no need to use gaseous carbon dioxide in the production of the superbasic zinc soaps. There is also no need to use special promoters to facilitate the binding of carbon dioxide. In addition, according to the invention, the reaction is carried out in a melt of zinc hydroxycarbonate and organic carboxylic acids. Accordingly, there is no need either for a solvent to be used and subsequently removed.
Basic zinc carbonate is formed when neutral zinc carbonate, ZnCO3, is reacted with water. Basic zinc carbonate occurs naturally as hydrozincite with the composition Zn5[(OH)3(CO3)]2, but is also commercially available.
As already mentioned, the process according to the invention is carried out at temperatures in the range from 100 to 200xc2x0 C. In a preferred embodiment, it is carried out at temperatures of 110 to 160xc2x0 C. and more particularly at temperatures of 130 to 150xc2x0 C.
As already mentioned, organic carboxylic acids containing 6 to 22 carbon atoms are used in the process according to the invention. These acids may be saturated or unsaturated, linear or branched. They may be used either individually or as a mixture of two or more fatty acids. Examples of suitable organic carboxylic acids containing 6 to 22 carbon atoms are caproic acid, oenanthic acid, caprylic acid, pelargonic acid, capric acid, undecanoic acid, lauric acid, tridecanoic acid, myristic acid, pentadecanoic acid, palmitic acid, heptadecanoic acid, stearic acid, nonadecanoic acid, arachic acid, heneicosanoic acid, behenic acid, 10-undecenoic acid, lauroleic acid, myristoleic acid, palmitoleic acid, oleic acid, petroselic acid, elaidic acid, ricinoleic acid, 12-hydroxystearic acid, 9,10-dihydroxystearic acid, 9,10,11,12-tetrahydroxystearic acid, linoleic acid, linolaidic acid, linolenic acid, elaeostearic acid, gadoleic acid, arachidonic acid, erucic acid, brassidic acid, clupanodonic acid.
One embodiment is characterized by the use of one or more organic carboxylic acids containing 6 to 22 carbon atoms, the content of linear carboxylic acids being at least 90% by weight, based on the total quantity of carboxylic acids used. At least 60% by weight of these linear carboxylic acids are saturated.
Another embodiment is characterized by the use of one or more organic carboxylic acids containing 6 to 22 carbon atoms, the content of acids branched at C-2 being at least 90% by weight, based on the total quantity of carboxylic acids used. 2-Ethylhexanoic acid is preferably used.
Basically, the are no limitations to the ratio in which the two reaction components, i.e. on the one hand the zinc hydroxycarbonate and on the other hand the organic carboxylic acids, are reacted with one another in the process according to the invention. However, the two components are preferably used in such a quantity that the equivalent ratio of OH to COOH is in the range from 0.5:1 to 10:1 and more particularly in the range from 0.5:1 to 2:1. In one particularly preferred embodiment, an equivalent ratio of about 1:1 is adjusted.
The expression xe2x80x9cequivalent ratioxe2x80x9d is familiar to the expert. The basic concept behind the notion of equivalence is that, for every substance involved in a reaction, the reactive groups participating in that reaction are considered. The indication of an equivalent ratio expresses the numerical ratio which all the reactive groups of the compounds used bear to one another. In the present case, this means the following: basic zinc carbonate is represented by the formula [ZnCO3]2x[Zn(OH)2]3. The organic carboxylic acids are represented by the formula C5-21xe2x80x94COOH where C5-21 is an alkyl group containing 5 to 21 carbon atoms. An equivalent OH:COOH ratio of 1:1 thus means that the basic zinc carbonate is reacted with the organic carboxylic acid in such a quantity ratio that there are as many OH groups in the zinc hydroxycarbonate used as there are COOH groups in the organic carboxylic acid used. Since, according to the above formula, basic zinc carbonate contains six OH groups, whereas the organic carboxylic acid contains only one COOH group, basic zinc carbonate and organic carboxylic acid must be used in a molar ratio of 1:6.
The present invention also relates to superbasic zinc soaps obtainable by reacting basic zinc carbonate with organic carboxylic acids containing 6 to 22 carbon atoms at temperatures in the range from 100 to 200xc2x0 C. in the absence of organic solvents and distilling off the water of reaction formed, the content of linear acids being at least 90% by weight, based on the total quantity of carboxylic acids used, and at least 60% by weight of these linear acids being saturated.
The present invention also relates to the use of the superbasic zinc soaps obtainable by the process according to the invention as additives for the processing of plastics and, more particularly, for stabilizing halogen-containing plastics against thermal and/or photochemical degradation.
The superbasic zinc soaps obtainable by the process according to the invention are suitable as additives for stabilizing halogen-containing organic plastics, more especially polyvinyl chloride (PVC).